Printing ink jet image with ink of cationic colorant and colorless ink of anionic polymer

ABSTRACT

This invention relates to method of printing an ink jet image using an ink jet ink set comprising a colored aqueous ink and a substantially colorless aqueous ink, wherein the colored ink comprises a cationic coloring agent and the colorless ink comprises an anionic polymer or oligomer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 11/094,150, filed Mar. 30,2005 U.S. Pat. No. 7,537,650.

FIELD OF THE INVENTION

This invention relates to a method of ink jet printing and particularlyto the imagewise admixture of inks having cationic colorants and inkshaving anionic polymeric agents thereby enabling the formation of highand consistent density independent of the media employed.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by thedeposition of ink droplets in a pixel-by-pixel manner to animage-recording element in response to digital signals. There arevarious methods that may be utilized to control the deposition of inkdroplets on the image-recording element to yield the desired image. Inone process, known as continuous inkjet, a continuous stream of dropletsis charged and deflected in an imagewise manner onto the surface of theimage-recording element, while unused droplets are caught and returnedto an ink sump. In another process, known as drop-on-demand ink jet,individual ink droplets arc projected as needed onto the image-recordingelement to form the desired image. Common methods of controlling theprojection of ink droplets in drop-on-demand printing includepiezoelectric transducers and thermal bubble formation. Ink jet printershave found broad applications across markets ranging from industriallabeling to short run printing to desktop document and pictorialimaging.

The inks used in the various inkjet printers can be classified as eitherdye-based or pigment-based. A dye is a colorant, which is dissolved inthe carrier medium. A pigment is a colorant that is insoluble in thecarrier medium, but is dispersed or suspended in the form of smallparticles, often stabilized against flocculation and settling by the useof dispersing agents. The carrier medium can be a liquid or a solid atroom temperature in both cases. Commonly used carrier media includewater, mixtures of water and organic co-solvents and high boilingorganic solvents, such as hydrocarbons, esters, ketones, etc.

Bishop and Czekai in U.S. Pat. No. 5,679,138 describe the preparationand use of micro-milled pigments and carbons employing anionicdispersing agents. These micro-milled pigments are particularly usefulin ink-jet printing because of their small particle size. Only anioniccharge stabilized pigments are described. More recently, the preparationof covalently functionalized (self-dispersed) pigments and carbonssuitable for ink jet printing have been described, inter alia, byBelmont in U.S. Pat. No. 5,554,739, Adams and Belmont in U.S. Pat. No.5,707,432, Johnson and Belmont in U.S. Pat. Nos. 5,803,959 and 5,922,118and in published applications WO 96/18695, WO 96/18696, WO 96/18689, WO99/51690, WO 00/05313, and WO 01/51566. These publications furtherdescribe the preparation and use of ink-jet inks employing the describedself-dispersed pigments. Both anionic and cationic self-dispersedpigments are described. Takada et al in U.S. Pub App 2002/0059883described the advantages of further stabilizing cationic self-dispersedpigments with acid components. Miyabayashi, in U.S. publishedapplication 2002/0077385 describes employing distinct colored inks, eachink employing differently colored anionic polymer stabilized coloringmaterials or cationic polymer stabilized coloring materials in distinctink-jet printing channels to control inter-color bleed. Katsuragi etal., in EP 1090966 and Kashiwazaki et al., in U.S. Pat. No. 6,399,674describe employing distinct colored inks, each ink employing differentlycolored anionic polymer stabilized coloring materials, anionic dyes orcationic polymer stabilized coloring materials or cationic dyes indistinct ink-jet printing channels to control inter-color bleed.Earlier, Pearlstine et al. in U.S. Pat. No. 5,518,534, Looman in U.S.Pat. No. 5,679,143, Shields and Radke in U.S. Pat. No. 5,428,383 andU.S. Pat. No. 5,488,402, Wang in U.S. Pat. No. 5,772,742 and Gundlach etal., in U.S. Pat. No. 6,039,793 described approaches to control colorbleed between image regions having distinct colored inks applied. Suchapproaches included pH adjustment or addition of multivalent metallicions to individual colored inkjet inks. While these approaches appear toimprove the inter-color bleed problem, the formation of high, uniformand consistent single color densities on a variety of plain papers aswell as designed ink-jet papers have not been adequately addressed.

SUMMARY OF THE INVENTION

This invention provides an ink jet ink set comprising a colored aqueousink and a substantially colorless aqueous ink, wherein the colored inkcomprises a cationic coloring agent and the colorless ink comprises ananionic polymer or oligomer.

This invention further provides a method of printing an ink jet imagecomprising separately applying to an ink jet receiver a colored ink anda substantially colorless ink, wherein the colored ink comprises acationic coloring agent and the colorless ink comprises an anionicpolymer or oligomer, and wherein the inks are applied in substantiallyan overlaying manner.

Use of the described combinations enables the formation of high, uniformand consistent single color densities across a variety of plain papers.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is in no way limited by the following theory, theinventors believe the mixing of both cationic and anionic chargedmaterial during application to the media enables consistent single colordensity on a variety of papers, particularly plain papers. Modern plainpapers tend to be anionic in characteristic while historic plain papersand designed ink-jet media tend to be cationic in character.Accordingly, anionic charged ink components will adhere well to historicplain papers and designed ink-jet media while cationic charged inkcomponents will adhere well to modern plain papers. Mixtures of bothanionic and cationic charged ink components will adhere to one anotheron mixture, forming mixed complexes and at least one of the two inkswill adhere well to both plain paper and designed ink-jet media thusbinding the formed complexes to the media.

In general, the colored ink jet ink composition consists of an aqueousvehicle which functions as a carrier, and a coloring agent. Additivesand/or co-solvents can be incorporated in order to adjust the ink toattain the desired performance, and will be described in detail laterherein.

The term ‘coloring agent’ as used herein may refer to just a colorant,or it may refer to a colorant in combination with, for example, adispersant of some kind. The colorants used herein are dyes or pigments,more preferably pigments. The colorant may be any color, but preferablythe colorant is cyan, magenta, yellow or black. The coloring agentgenerally comprises a colorant which may be self-dispersed,polymer-dispersed or surfactant dispersed. When the colorant isself-dispersed the colorant is synonymous with the coloring agent.

Self-dispersed pigment refers to pigments that have been chemicallymodified with a charge or a polymeric group, wherein the chemicalmodification aids the pigment in becoming and/or substantially remainingdispersed in a liquid vehicle. When the pigment is a self-dispersingpigment the charging moiety is covalently linked to the pigment. As usedherein, polymer-dispersed pigment refers to pigments that utilize apolymer or an oligimer dispersant and/or pigments that utilize a polymeror oligimer physical coating to aid the pigment in becoming and/orsubstantially remaining dispersed in a liquid vehicle. When the coloringagent is a polymer-dispersed pigment, the polymer may provide thecationic charge. Surfactant-dispersed pigment refers to pigments thatutilize a surfactant dispersant to aid the pigment in becoming and/orsubstantially remaining dispersed in a liquid vehicle. When the coloringagent is a surfactant-dispersed pigment, the surfactant may provide thecationic charge. It is also possible that both the pigment and thesurfactant or polymer are charged, or that the pigment is charged andthe polymer or surfactant are not. What is necessary is that the“charge” remain “available” for interaction with other components onmixing i.e. that the charge is not masked. Normally for a polymer- orsurfactant-dispersed pigment, the charge would be provided by thepolymer or the surfactant.

The colorant may be chosen from a wide range of conventional coloredcolorants, preferably pigments. Preferably, the pigment is a whitepigment, a black pigment, a blue pigment, a brown pigment, a cyanpigment, a green pigment, a violet pigment, a magenta pigment, a redpigment, or a yellow pigment, or shades or combinations thereof.Suitable classes of colored pigments include, for example,anthraquinones, phthalocyanine blues, phthalocyanine greens, diazos,monoazos, pyranthrones, perylenes, heterocyclic yellows, quinacridones,diketopyrolo-pyroles, and (thio)indigoids. Representative examples ofphthalocyanine blues include copper phthalocyanine blue and derivativesthereof (Pigment Blue 15). Representative examples of quinacridonesinclude Pigment Orange 48, Pigment Orange 49, Pigment Red 122, PigmentRed 192, Pigment Red 202, Pigment Red 206, Pigment Red 207, Pigment Red209, Pigment Violet 19 and Pigment Violet 42. Representative examples ofanthraquinones include Pigment Red 43, Pigment Red 194 (Perinone Red),Pigment Red 216 (Brominated Pyanthrone Red) and Pigment Red 226(Pyranthrone Red). Representative examples of perylenes include PigmentRed 123 (Vermillion), Pigment Red 149 (Scarlet), Pigment Red 179(Maroon), Pigment Red 190 (Red), Pigment Violet, Pigment Red 189 (YellowShade Red) and Pigment Red 224. Representative examples of thioindigoidsinclude Pigment Red 86, Pigment Red 87, Pigment Red 88, Pigment Red 181,Pigment Red 198, Pigment Violet 36, and Pigment Violet 38.Representative examples of heterocyclic yellows include Pigment Yellow1, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, PigmentYellow 14, Pigment Yellow 17, Pigment Yellow 65, Pigment Yellow 73,Pigment Yellow 74, Pigment Yellow 110, Pigment Yellow 117, PigmentYellow 128, Pigment Yellow 138, Pigment Yellow 151 and Pigment Yellow155. A representative example of diketopyrolo-pyroles include PigmentRed 254. Such pigments are commercially available in either powder orpress cake form from a number of sources including, BASF Corporation,Engelbard Corporation and Sun Chemical Corporation. Examples of othersuitable colored pigments are described in the Colour Index, 3rd edition(The Society of Dyers and Colourists, 1982). Representative examples ofblack pigments include various carbon blacks (Pigment Black 7) such aschannel blacks, furnace blacks and lamp blacks, and include, forexample, carbon blacks sold under the Regal®, Black Pearls®, Elftex®,Monarch®, Mogul®, and Vulcan® trademarks available from CabotCorporation (such as Black Pearls® 2000, Black Pearls® 1400, BlackPearls®1300, Black Pearls® 1100, Black Pearls® 1000, Black Pearls® 900,Black Pearls® 880, Black Pearls® 800, Black Pearls® 700, Black Pearls®L,Elftex® 8, Monarch® 1400, Monarch® 1300, Monarch®1100, Monarch® 1000,Monarch® 900, Monarch®880, Monarch® 800, Monarch® 700, Mogul®L, Regal®330, Regal® 400, Vulcan®P). Other suitable carbon blacks include, butare not limited to, Printex 40, Printex 80, Printex 300, Printex L,Printex U, Printex V, Special Black 4, Special Black 5, FW200, (theforegoing available from Degussa Corporation), Raven 780, Raven 890,Raven 1020, Raven 1040, Raven 1255, Raven 1500, Raven 5000, Raven 5250(the foregoing available from Columbian Chemical Corporation) and MA100and MA440 available from Mitsubishi Chemical Corporation.

Other suitable pigments within the scope of the present inventioninclude carbon products such as graphite, carbon black, vitreous carbon,carbon fibers, activated charcoal, and activated carbon. The carbon maybe of the crystalline or amorphous type. Finely divided forms of theabove are preferred; also, it is possible to utilize mixtures ofdifferent carbons.

Preferred pigments include those that comprise at least one metal thatis not a divalent metal. Examples include, but are not limited to,phthalocyanine pigments containing aluminum, zinc, magnesium, or iron.

The pigments will typically have a wide range of BET surface areas, asmeasured by nitrogen adsorption. Preferably, the pigment has a surfacearea equal to or greater than 10 m²/g, and more preferably equal to orgreater than and 100 m²/g, thereby corresponding to a smallerprimary/aggregate particle size. Such surface areas have been found toprovide for a more uniform distribution and efficient level of treatingagent on the pigment and a higher percent yield of the modified pigmentafter post processing techniques. If the preferred higher surface areaof the pigment (thereby corresponding to a smaller particle size) is notreadily available, it is well recognized by those skilled in the artthat the pigment may be subjected to conventional size comminution orreduction techniques, such as ball or jet milling, to reduce the pigmentto the desired particle size.

The ink compositions employing self-dispersed pigments used in thepresent invention include at least one modified pigment having attachedat least one organic group. The organic group may vary depending on thevehicle used for the ink composition as well as on the desired ink andprint performance properties. This allows for greater flexibility bytailoring the pigment to the specific application.

In one embodiment, the organic group comprises an ionic group, anionizable group, or a mixture of an ionic group and an ionizable group.An ionic group is cationic and is associated with a counterion of theopposite charge including inorganic or organic counterions such asacetate, NO₃ ⁻, SO₄ ⁻², R′SO₃ ⁻, R′OSO₃ ⁻, OH⁻, and Cl⁻ where R′represents hydrogen or an organic group such as a substituted orunsubstituted aryl and/or alkyl group. An ionizable group is one that iscapable of forming an ionic group in the medium of use. Thus, in apreferred embodiment, the organic group is an organic ionic group.Organic ionic groups include those described in U.S. Pat. No. 5,698,016,the description of which is fully incorporated herein by reference.

Positively charged organic ionic groups may be generated from protonatedamines that are attached to the pigment. Preferably, an organic grouphaving an amine substituent has a pKb of less than 5. Positively chargedorganic ionic group may be quaternary ammonium groups (—NR′₃ ⁺) andquaternary phosphonium groups (—PR′₃ ⁺), where R′ represents hydrogen oran organic group such as a substituted or unsubstituted aryl and/oralkyl group. For example, amines may be protonated to form ammoniumgroups in acidic media. Quaternized cyclic ammonium ions, andquaternized aromatic ammonium ions, can also be used as the organicionic group. Thus, N-substituted pyridinium species, such asN-methyl-pyridyl, can be used in this regard. Examples of cationicorganic groups include, but are not limited to, -3-C₅H₄N(C₂H₅)⁺,-3-C₅H₄N(CH₃)⁺, -3-C₅H₄N(CH₂C₆H₅)⁺, —C₆H₄(NC₅H₅ ⁺), —C₆H₄COCH₂N(CH₃)₃ ⁺,—C₆H₄COCH₂(NC₅H₅)⁺, —C₆H₄SO₂ NH(C₄H₃N₂H⁺), —C₆H₄NH₃ ⁺, —C₆H₄NH₂(CH₃)⁺,—C₆H₄NH(CH₃)₂ ⁺, —C₆H₄N(CH₃)₃ ⁺, —C₆H₄CH₂NH₃ ⁺, —C₆H₄CH₂NH₂(CH₃)⁺,—C₆H₄CH₂NH(CH₃)₂ ⁺, —C₆H₄CH₂N(CH₃)₃ ⁺, —C₆H₄CH₂CH₂NH₃ ⁺,—C₆H₄CH₂CH₂NH₂(CH₃)⁺, —C₆H₄CH₂CH₂NH(CH₃)₂ ⁺ and —C₆H₄CH₂CH₂N(CH₃)₃ ⁺.Other substituted or unsubstituted arylene or heteroarylene groups canbe used in the place of the C₆H₄ groups shown in the structures above.Preferably, the cationic organic group is —NR′₃ ⁺ wherein R′ is an alkylgroup or an aryl group. Another preferred group is —C₅H₄N—R′⁺, whereinR′ is an alkyl group such as a methyl group or a benzyl group.

In another embodiment, the organic group attached to the modifiedpigments used in the method of the present invention may also bepolymeric. The attached polymer groups may be present as individualattached chains or as a coating on the pigment, as is described below.

For example, the organic group attached to the modified pigments maycomprise a pigment having attached at least one organic grouprepresented by the formula —X-Sp-[Polymer]R, wherein X, which isdirectly attached to the pigment, represents an aryl or heteroaryl groupor an alkyl group and is substituted with an Sp group, Sp represents aspacer group, the group Polymer represents a polymeric group comprisingrepeating monomer groups or multiple monomer groups or both, and Rrepresents hydrogen, a bond, a substituted or unsubstituted alkyl group,or a substituted or unsubstituted aryl group. The group Polymer can besubstituted or unsubstituted with additional groups. The total number ofmonomer repeating units that comprise the “polymer” is not greater thanabout 500 monomer repeating units.

The group Polymer can be any polymeric group capable of being attachedto a pigment. Thus, for example, the group Polymer can be athermoplastic polymeric group or a thermosetting polymeric group.Further, the polymeric group can be a homopolymer or copolymer. Further,the group Polymer can be any type of polymeric group, such as a randompolymer, alternating polymer, graft polymer, block polymer, star-likepolymer, and/or comb-like polymer. The group Polymer can also be one ormore polyblends. The group Polymer can be an interpenetrating polymernetwork (IPN); simultaneous interpenetrating polymer network (SIN); orinterpenetrating elastomeric network (IEN).

For the group Polymer, examples include, but are not limited to,linear-high polymers such as polyethylene, poly(vinylchloride),polyisobutylene, polystyrene, polycaprolactam (nylon), polyisoprene, andthe like. Other general classes are polyamides, polycarbonates,polyelectrolytes, polyesters, polyethers, (polyhydroxy)benzenes,polyimides, polymers containing sulfur (such as polysulfides,(polyphenylene) sulfide, and polysulfones), polyolefins,polymethylbenzenes, polystyrene and styrene copolymers (ABS included),acetal polymers, acrylic polymers, acrylonitrile polymers andcopolymers, polyolefins containing halogen (such as polyvinyl chlorideand polyvinylidene chloride), fluoropolymers, ionomeric polymers,polymers containing ketone group(s), liquid crystal polymers,polyamide-imides, polymers containing olefinic double bond(s) (such aspolybutadiene and polydicyclopentadiene), polyolefin copolymers,polyphenylene oxides, poly(vinyl alcohols), polyurethanes, thermoplasticelastomers, and the like. Preferably at least some of these monomerunits of the group Polymer comprise an ionic group, an ionizable group,or a mixture of ionic or ionizable groups. Additional examples thereofmay include those obtained by polymerization of a vinyl monomer andhaving a cationic nature in at least a part of the resulting polymer.Examples of a cationic monomer for forming the cationic moiety includesalts of such tertiary amine monomers as described below, andquaternized product thereof. Namely, there are mentioned:N,N-dimethylaminoethyl methacrylate, N,N-dimethyl-aminoethyl acrylate,N,N-dimethyl aminopropyl methacrylate, N,N-dimethylaminopropyl acrylate,N,N-dimethylacrylamide, N,N-dimethylmethacrylamide,N,N-dimethylaminoethylacrylamide, N,N-dimethylaminoethylmethacrylamide,N,N-dimethylaminopropylacrylamide, andN,N-dimethylaminopropyl-methacrylamide. In the case of a tertiary amine,examples of a compound for forming a salt include hydrochloric acid,sulfuric acid and acetic acid. Examples of a compound used inquaternization include methyl chloride, dimethylsulfuric acid, benzylchloride and epichlorohydrin. Among these, methyl chloride anddimethylsulfuric acid are preferred for preparing a dispersing agentused in the present invention. Such tertiary amine salts or quaternaryammonium compounds as described above behave as a cation in water, andunder neutralized conditions, they are stably soluble in an acidicregion. The content of these monomers in the copolymer is preferablywithin a range of from 20 to 60% by weight. Examples of other monomersused in the formation of the above-described high-molecular dispersingagents include hydrophobic monomers, for example, acrylic esters havinga hydroxyl group, such as 2-hydroxyethyl methacrylate; and acrylicesters having a side chain of long ethylene oxide chain; and styrenemonomers, and water-soluble monomers soluble in water at a pH of about 3to 10, such as acrylamides, vinyl ethers, vinylpyrrolidones,vinylpyridines and vinyloxazolidines. As the hydrophobic monomers,styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalenederivatives, (meth)acrylic acid alkyl esters and acrylonitrile can beused. In the high-molecular dispersing agent obtained by thecopolymerization, the water-soluble monomer be used in the range of from15 to 35% by weight for the stability of the copolymer in an aqueoussolution, and the hydrophobic monomer be used in the range of from 20 to40% by weight for enhancing the dispersing effect of the copolymer tothe pigment.

The group Sp represents a spacer group as described above. Spacer group,as used herein, is a link between two groups and can be a bond, or achemical group such as, but not limited to, esters such as —CO₂— and—O₂C—, sulfones such as —SO₂— and —SO₂C₂H₄—, ketones such as —C(O)—,amide derivatives such as —NRC(O)—, —C(O)NR—, —NRCO₂—, —O₂CNR—, and—NRC(O)NR—, sulfonates, sulfonamides, —O—, —S—, amines such as —NR,imides, arylene groups, alkylene groups, and the like, wherein R, whichcan be the same or different, represents hydrogen or an organic groupsuch as a substituted or unsubstituted aryl and/or alkyl group.

The group X represents an aryl or heteroaryl group or an alkyl group. Xis directly attached to the pigment and is further substituted with anSp group. The aromatic group can be further substituted with any group,such as one or more alkyl groups or aryl groups. Preferably, the aryl orheteroaryl group is phenyl, naphthyl, anthracenyl, phenanthrenyl, orbiphenyl, and the heteroaryl group is pyridinyl, benzothiadiazolyl, orbenzothiazolyl. When X represents an alkyl group, examples include, butare not limited to, substituted or unsubstituted alkyl groups which maybe branched or unbranched. The alkyl group can be substituted with oneor more groups, such as aromatic groups. Preferred examples include, butare not limited to, C₁-C₁₂ groups like methyl, ethyl, propyl, butyl,pentyl, or hexyl groups. Preferably, X is an aryl group.

The group X may be substituted with one or more functional groups.Examples of functional groups include, but are not limited to, R′″,OR′″, COR′″, COOR′″, OCOR′″, carboxylates, halogens, CN, NR′″₂, SO₃H,sulfonates, sulfates, NR′″(COR′″), CONR′″₂, NO₂, PO₃H₂, phosphonates,phosphates, N═NR′″, SOR′″, NSO₂R′″, wherein R′″ which can be the same ordifferent, is independently hydrogen, branched or unbranched C₁-C₂₀substituted or unsubstituted, saturated or unsaturated hydrocarbons,e.g., alkyl, alkenyl, alkynyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedalkaryl, or substituted or unsubstituted aralkyl.

As shown by the structures above, the group Polymer is attached to thepigment through the spacer group Sp. However, it will also be recognizedthat when R represents a bond, the available bond can also be attachedto the pigment. In addition, the group Polymer can also be attached tothe pigment at multiple points along the polymer chain through properchoice of substituent groups on the repeating monomer units. Thesesubstituents may also comprise spacer groups or —X-Sp-groups asdescribed above. Thus, these groups can be attached to the pigment ateither end or at points along the backbone. Further, these groups can beany type of polymeric group, such as a random polymer, alternatingpolymer, graft polymer, block polymer, star-like polymer, and/orcomb-like polymer.

As another example, the polymer group attached to the pigment can alsobe directly attached. Thus, the polymer can be attached either through acovalent or ionic bond. The amount of polymer present on the modifiedpigments can be high enough to cover a substantial amount of thepigment. Thus, in another embodiment, the modified pigment products usedin the method of the present invention comprise a pigment that is atleast partially coated with one or more polymeric coatings and can besubstantially or fully coated by one or more polymers. The use of theterm “coated” includes both partially and fully coated pigments andmodified pigments—the polymer partially or fully encapsulates themodified pigment, wherein the modified pigment is the core and thepolymer is the shell. The polymer(s) coated onto or used to encapsulatethe modified pigment is preferably present on the modified pigment suchthat the polymer(s) is not substantially extractable by an organicsolvent. More preferably, the polymer(s) on the modified pigment isattached by physical (for example, adsorption) and/or chemical means(for example, bonding or grafting).

Further details concerning the polymer coated pigments and methods ofmaking them are set forth in International Published Application No. WO00/22051, incorporated in its entirety by reference herein.

In another preferred embodiment, the attached organic group is a dye.These attached dye organic groups are similar to those that aretraditionally used as colorants in ink compositions. Attached dyesinclude, but are not limited to, food dyes, FD&C dyes, derivatives ofphthalocyanine tetrasulfonic acids, including copper phthalocyaninederivates, tetra sodium salts, tetra ammonium salts, tetra potassiumsalts, tetra lithium salts, and the like. Attached dyes can, forexample, provide the ability to modify color balance and adjust opticaldensity while at the same time maintaining and/or providing pigmentstability.

The amount of attached organic groups, whether ionic, ionizable, orpolymeric, employed with charged pigments useful in the presentinvention can be varied in order to attain desired performanceattributes, such as dispersibility in the ink vehicle and printwater-fastness and smear-fastness. In addition, modified pigmentproducts comprising multiple attached organic groups can result inimproved properties. In general, the amount of attached organic groupsis from about 0.01 to about 10.0 micromoles of organic group per m²surface area of pigment, as measured by nitrogen adsorption (BETmethod). For example, the amount of attached organic groups is betweenfrom about 0.5 to about 4.0 micromoles per m².

The modified pigments used in the method of the present invention aremodified using methods known to those skilled in the art such thatorganic groups are attached to the pigment. This provides a more stableattachment of the groups onto the pigment compared to adsorbed groups,such as polymers, surfactants, and the like. For example, the modifiedpigments used in the method of the present invention can be preparedusing the methods described in U.S. Pat. Nos. 5,554,739; 5,851,280;6,042,643; 5,707,432; and 5,837,045, and PCT Publication WO 99/23174,the descriptions of which are fully incorporated herein by reference.

The modified pigments can be purified by washing, such as by filtration,centrifugation, or a combination of the two methods, to remove unreactedraw materials, byproduct salts and other reaction impurities. Theproducts may also be isolated, for example, by evaporation or it may berecovered by filtration and drying using known techniques to thoseskilled in the art. Dispersions of the pigments may be further purifiedor classified to remove impurities and other undesirable free speciesthat can co-exist in the dispersion as a result of the manufacturingprocess. For example, the dispersion can be purified to remove anyundesired free species, such as unreacted treating agent. Knowntechniques of ultrafiltration/diafiltration using a membrane or ionexchange may be used to purify the dispersion and remove a substantialamount of free ionic and unwanted species. An optional exchange ofcounterions step may also occur in the purification process whereby thecounterions that form a part of the modified pigment are exchanged orsubstituted with alternative counterions (including, e.g., amphiphilicions) utilizing known ion exchange techniques such as ultrafiltration,reverse osmosis, ion exchange columns and the like. Particular examplesof counterions that can be exchanged include, but are not limited toCl⁻, NO₃ ⁻, NO₂ ⁻, acetate and Br⁻.

The ink compositions can be formed with a minimum of additionalcomponents (additives and/or cosolvents) and processing steps. Themodified pigment is present in the ink compositions in an amounteffective to provide the desired image qualities (for example, opticaldensity) without detrimentally affecting the performance of the ink. Forexample, typically, the modified pigment will be present in an amountranging from about 1% to about 20% based on the weight of the ink. It isalso within the bounds of the present invention to use a formulationcontaining a mixture of unmodified pigments with the modified pigmentsdescribed above.

The ink compositions can be further purified and/or classified usingmethods such as those described above for the modified pigments anddispersions thereof. An optional counterion exchange step can also beused. In this way, unwanted impurities or undesirable large particlescan be removed to produce ink with good overall properties.

Polymeric and oligimeric dispersed pigments useful in the presentinvention can employ the same or similar charged polymeric materials asdescribed above. Here the charged polymers or oligimer are employed as adispersing agent for pigment. Any water-soluble resin may be used so faras it can disperse a pigment stably in water or an aqueous medium by theaction of a cationic group. However, those having a weight averagemolecular weight ranging from 1,000 to 30,000, more preferably from3,000 to 15,000 are particularly preferred. Specific examples of suchwater-soluble resins include block copolymers, graft copolymers andrandom copolymers composed of at least two monomers selected fromhydrophobic monomers such as styrene, styrene derivatives,vinylnaphthalene, vinylnaphthalene derivatives and aliphatic alcoholesters of alpha, beta.-ethylenically unsaturated amines and hydrophilicmonomers such as ammonium and phosphonium salts and derivatives thereof,and salts of these copolymers. These resins are acid soluble resins thatdissolve in an aqueous solution of an acid.

Besides, homo-polymers composed of a hydrophilic monomer, water solublepolymers or salts thereof may also be used. These water-soluble resinsare preferably used within a range of from 0.1 to 5% by weight based onthe total weight of the ink.

The pigment inks used in the present invention are prepared bydispersing or dissolving such pigment and water-soluble resin asdescribed above in an aqueous medium. The aqueous medium preferably usedin the pigment inks is a mixed solvent of water and a water-solubleorganic solvent. As the water, it is preferable to use ion-exchangedwater (deionized water) instead of tap water containing various ions.

Surfactant dispersed pigments employ low molecular weight surface-activeagents as dispersants. Any cationically charged low molecular weightsurface active agent known in the art can be employed to dispersepigments in a manner useful in the practice of the invention. Examplesof cationic surfactants useful in this regard include but are notlimited to mono-, di-, tri- and tetraalkyl ammonium salts, mono-, di-,tri- and tetraryl ammonium salts, mixed alkyl-aryl ammonium salts, thecorresponding alkyl and aryl phosphonium salts, pyridinium salts, andheterocyclic ammonium salts. Also useful are lower molecular weightamins oligimers such as polyethylene imine salts, polyallyl amine salts,polyvinyl amine salts and the like. Specific examples of low molecularweight surface-active agent include but are not limited to oleoylammonium chloride, and cetyl trimethyl ammonium bromide and so forth.Cationic surfactants can be employed in this manner. The used amount ofsuch a cationic charged substance as described above is preferablywithin a range of from 0.05 to 10% by weight, more preferably from 0.05to 5% by weight based on the total weight of the ink.

Useful dyes having a cationic charge may include any suitable cationicdye known in the art. These include but are not limited to thosedescribed in WO 95/01772, WO 95/15144, EP 714 954, EP 318 294, in theColor Index. 4^(th) ed. The Society of Dyers and Colorists, London, andin Broadbent, A. D., Basic Principles of Textile Coloration. Chap 17;Cationic Dyes, The Society of Dyers and Colorists, London (2001).Specifically useful dyes include Rhodamine B (RB), Crystal Violet (CV),Cationic Yellow Y-13, Cationic Golden Yellow Y-28, Vationic BrilliantYellow Y-40, Cationic Yellow Y-51, Cationic Dark Brown X-3RL, CationicPink R-13, Cationic Brilliant Red R-14, Cationic Red R-46, Cationic RedViolet V-16, Cationic Turquoise Blue B-03, Cationic Blue B-41, CationicBlue B-66 and Cationic Blacks.

Any ordinary dispersing machine may be employed as a dispersing machineto prepare the pigment ink. Examples thereof include ball mills, sandmills, etc. Of these mills, a high-speed sand mill may preferably beused, such as Super Mill, Sand Grinder, Beads Mill, Agitator Mill, GrainMill, Dyno Mill, Pearl Mill and Coball Mill (all are trade names).

In addition, if necessary, additives, such as water-soluble organicsolvents, surface active agents, pH adjusting agents, rust preventives,fungicides, antioxidants, evaporation accelerators, chelating agents,and water-soluble polymers other than the above described components,may be added into inks used in the present invention.

Any water soluble organic solvents known in the ink are can be employedin the inks useful in the present invention. Examples of thewater-soluble organic solvent used herein include amides such asdimethylformamide and dimethylacetamide; ketones such as acetone; etherssuch as tetrahydrofuran and dioxane; polyalkylene glycols such aspolyethylene glycol and polypropylene glycol; alkylene glycols such asethylene glycol, propylene glycol, butylene glycol, triethylene glycol,1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol;lower alkyl ethers of polyhydric alcohols, such as ethylene glycolmethyl ether, diethylene glycol monomethyl ether and triethylene glycolmonomethyl ether; monohydric alcohols such as methyl alcohol, ethylalcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butylalcohol, tert-butyl alcohol, and lower alkyl ethers of polyhydricalcohol, such as, glycerine, ethylene glycol monomethyl (or ethyl)ether,diethylene glycol monomethyl (or ethyl)ether, etc.; glycerol, cyclicamide compounds, such as, N-methyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone, sulfolane, dimethyl sulfo oxide,2-pyrolidone, epsilon caprolactam, etc.; and imido compounds, such assuccinimide etc., triethanolamine, sulfolane and dimethyl sulfoxide. Noparticular limitation is imposed on the content of the water-solubleorganic solvent. However, it is preferably within a range of from 5 to60%, more preferably from 5 to 40% based on the total weight of theliquid composition. Moreover, when a range of 30 to 95 weight % isadopted as a content of water in ink, good solubility of a coloringmaterial is acquired, increase in viscosity of ink is suppressed, andfixing characteristics can fully be satisfied.

Besides the above components, additives such as viscosity modifiers, pHadjustors, antiseptics, various surfactants, antioxidants, evaporationaccelerators, water-soluble cationic or anionic compounds commerciallyavailable water soluble-dye or the like and binder resins may besuitably incorporated as needed. The selection of the surfactants isparticularly important from the viewpoint of controlling thepenetrability of the liquid composition into a recording medium.

Any known cationic or neutral surfactant can be employed. Examples ofcationic surfactants include but are not limited to mono-, di-, tri- andtetraalkyl ammonium salts, mono-, di-, tri- and tetraryl ammonium salts,mixed alkyl-aryl ammonium salts, the corresponding alkyl and arylphosphonium salts, pyridinium salts, and heterocyclic ammonium salts.Examples of neutral nonionic surfactants include but are not limited topolyoxyethylene alkyl ethers, polyoxyethylene alkyl esters,polyoxyethylene sorbitan alkyl esters, lower alcohols, acetylenicalcohols and acetylene glycols. One or more of these surfactants may besuitable chosen for use. The amount of the surfactant used variesaccording to the kind of the dispersing agent used, but is desirablywithin a range of from 0.01 to 5% by weight based on the total weight ofthe ink. It is preferred that the amount of the surfactant added bedetermined in such a manner that the surface tension of the resultingink is at least 20 mN/m (dyne/cm), because the occurrence of deformedprinting (inaccurate ink landing) due to wetting of an orifice can beeffectively prevented in an inkjet recording system used in the presentinvention. Preferable physical properties of the liquid composition asdescribed above are, the surface tension in a range of from 10 to 70mN/m (dyn/cm), preferably 20 to 60 mN/m (dyn/cm), and the viscosity in arange of from 1 to 30 centipoise (cP) and preferably from 1.5 to 5centipoise. Inks comprising cationic charged pigments can be adjusted toa pH of between 1 and 7 and preferably between 3 and 5.

The binder resins may be used in combination within a limit not impedingthe texture of the recording medium used and the storage stability andejection stability of the liquid composition, for example, to furtherimprove the rub-off resistance of the cationic fine particles, and maybe freely selected from water-soluble polymers, emulsions, latexes, andso forth as known in the art.

The colorless ink jet ink composition of the invention comprises anaqueous medium and an anionic charged polymer or oligomer. Thesubstantially colorless ink can be further employed as a protective ink.A substantially colorless ink includes inks which may have some tintingto improve the color balance of the final image. However, bysubstantially colorless it is intended that such inks do not form theimage itself. Rather, they are used in combination to enhance thecoloring capability of a cationic charge colorant, and optionally as aprotective coating or to change or enhance the gloss of the final image.

The degree of anionic charge is quantified as the polymer acid number.Preferably the anionic polymer or oligomer in the colorless ink has aweight average molecular weight of 600 to 30,000. It is also preferredthat the anionic polymer or oligomer in the colorless ink has an acidnumber of 50 to 200. In one embodiment the anionic polymer is polyester,polyurethane or polymers derived from styrene and/or acrylic acidderivatives. In a preferred embodiment, the colorless ink jet inkcomposition of the invention comprises an aqueous medium and at leasttwo different anionic charged polymers, a first polymer and a secondpolymer, having a weight average acid number of 70 to 200. Thecomposition may also comprise one or more additional polymers providedthat the weight average acid number of all of the polymers is 70 to 200.The “weight average acid number” equals the weight percent of the 1^(st)polymer times the acid number of the 1st polymer+weight percent of the2^(nd) polymer times the acid number of the 2^(nd) polymer, etc. Thetotal weight percent of all polymers should equal 100 percent.Preferably at least two different polymers have a weight average acidnumber of 80 to 160. In a preferred embodiment the first polymer has anacid number of 60 to 100 and the second polymer has an acid number of180 to 240.

Examples of useful polymers include polyester, polyurethane or polymersderived from styrene and/or acrylic acid derivatives. Useful polymerswill be described in more detail below. Both condensation and additionpolymers arc useful. When at least two distinct polymers are employed,preferably the first polymer is a condensation polymer and the secondpolymer is an addition polymer. It is also preferred that the molecularweight of the polymer is independently within the range of 6,000 to30,000. In one embodiment of the invention the first polymer is acondensation polymer that has an acid number of 60 to 100 and amolecular weight of greater than 10,000, and the second polymer is anaddition polymer that has an acid number greater than 180 and amolecular weight of less than 18,000. It is particularly preferred thatthe first polymer is a polyurethane polymer and the second polymer is anacrylic polymer.

Examples of useful condensation polymers include polyesters,polycarbonates, polyamides, polyimides, polyurethanes, polyethers, andpolysiloxane. When the first polymer is a polyurethane, it has an acidnumber of 60 to 100, and preferably from 70 to 90. When used herein, theterm “acid number”, also known as “acid value”, is defined by the numberof milligrams of potassium hydroxide required to neutralize one gram ofpolymer. Thus, the acid number of a given polymer is related to thepercent of acid-containing monomer or monomers. The higher the acidnumber, the more acid functionality is present in the polymer. Theinventors have found that if the acid number is too high (greater than100), then the ink jet ink composition will not provide adequate stainprotection, and if the acid number is too low (less than 60), then thejettability of the ink composition using an ink jet printhead will becompromised, especially when using a thermal drop-on-demand printhead.

The invention preferably employs a polyurethane formed from at least onemonomer comprising at least two hydroxyl groups and another monomercomprising at least two isocyanate groups. The acid number of thepolyurethane is provided by acid groups that are, in turn, provided bythe at least one monomer comprising at least two hydroxyl groups. Theacid groups are preferably carboxylic acid groups, but any type of acidgroups may be used. Examples of monomers comprising at least twohydroxyl groups and at least one carboxylic acid group are2,2-bis(hydroxymethyl) propionic acid and the hydroxyethylether of4,4-bis(4-hydroxyphenyl)valeric acid. Other examples are described inU.S. Pat. No. 6,268,101 B1 and U.S. 2003/0184629 A1 and references citedtherein.

The polyurethanes are also preferably derived from a monomer having atleast two isocyanate groups; diisocyanates are typically used in the artof polyurethane chemistry, but triisocyanates may also be used. Examplesof diisocyanates include isophorone diisocyanate and others described inthe above references.

The polyurethanes used in the invention are optionally derived from anadditional monomer comprising at least two hydroxyl groups and which isdifferent from the monomer having at least two hydroxyl groups and atleast one carboxyl group. These optional monomers are typically highermolecular weight monomers having a molecular weight of less than 3000.They are often referred to in the art as polyols and examples includethose described in the above references. Examples include polyols andpolyhydroxy derivatives of polycarbonates, polyethers, polyesters,polyacetals, polyacrylates, polyester amides and polythioethers.Preferably the optional monomer is a polycarbonate. More preferably, theoptional monomer comprising at least two hydroxyl groups is apoly(hexamethylene carbonate) diol.

The polyurethane used in the invention has a weight average molecularweight, Mw, of greater than 10,000. If Mw is less than 10,000, then theink jet ink composition will not provide adequate stain and scratchresistance. The maximum Mw of the polyurethane is not particularlylimited, but is generally dictated by the physical property requirementsof the composition and the method by which it will be applied, asdiscussed below. If the ink composition is used as an ink jet ink for athermal printhead, then the maximum Mw of the polyurethane is preferably30,000.

Preferably the present invention employs at least one addition polymer(this term includes copolymers) formed from a mixture of vinyl orunsaturated monomers. Preferably the addition polymer has an acid number180 to 240, and more preferably of 200 to 240. Preferably the polymeralso has a weight average molecular weight less than 18,000, andpreferably in the range of 6,000 to 16,000. In one embodiment, themixture of monomers includes styrenic monomers. Preferred styrenicmonomers include, but are not limited to, d-alkylstyrenes,trans-β-alkylstyrenes, alkylstyrenes, alkoxystyrenes, halogenatedstyrenes, vinyl naphthalenes and mixtures thereof. Specific examples ofstyrenic derivatives include styrene, {acute over (α)}-methylstyrene,trans-β-methylstyrene, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 3-isopropyl styrene, 3-butyl styrene, 3-cyclohexyl styrene,3,4-dimethyl styrene. 3-chlorostyrene, 3,4-dichloro styrene,3,4,5-trichloro styrene, 3-bromo styrene, 3-iodo styrene, 3-fluorostyrene, 3-chloro-4-methyl styrene, benzyl styrene, vinyl naphthalene,divinylbenzene, methyl vinylbenzoate ester, vinylbenzoic acid, vinylphenol, 3-methoxy styrene, 3,4-dimethoxy styrene, 3-methyl-4-methoxystyrene, acetoxystyrene, acetoxymethylstyrene and (t-butoxycarbonyloxy)styrene. The styrenic monomers may be substituted with ionicfunctionalities such as sulfonate and carboxylate. Specific examplesinclude sodium styrenesulfonate and sodium vinylbenzoate.

In another embodiment, the mixture of monomers includes acrylicmonomers. The term “acrylic monomer” as employed herein includes acrylicacid, acrylate esters and derivatives and mixtures thereof. Examples ofacrylic acid monomers include but are not limited to alkylacrylic acids,3-alkylacrylic acids and 3-haloacrylic acids. Specific examples includecrotonic acid, cinnamic acid, citraconic acid, sorbic acid, fumaricacid, methacrylic acid, ethacrylic acid, 3-methylacrylic acid,3-chloroacrylic acid and 3-chloromethacrylic acid.

Examples of acrylate esters include but are not limited to alkylacrylates, aryl acrylates, alkyloxyalkyl acrylates, alkyloxyarylacrylates, hydroxyalkyl acrylates, hydroxyaryl acrylates, crotonicesters, cinnamic esters, citraconic esters, sorbic esters and fumaricesters. Specific examples include n-butyl acrylate, methyl acrylate,ethyl acrylate, n-propyl acrylate, isopropyl acrylate, amyl acrylate,hexyl acrylate, n-octyl acrylate, lauryl acrylate, 2-chloroethylacrylate, phenyl acrylate, benzyl acrylate, allyl acrylate, methyl3-chloroacrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate,2-(2-methoxyethoxy)ethyl acrylate, 2-ethoxyethyl acrylate,2-(2-ethoxyethoxyl)ethyl acrylate, 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, glycidyl acrylate, N,N-dimethylaminoethylacrylate, trifluoroethyl acrylate, 2-sulfoethyl acrylate and thecorresponding methacrylates.

Acrylic monomers useful in the present invention also includeunsaturated anhydride and unsaturated imide monomers which may becompletely or partially hydrolyzed after polymerization to form thecorresponding carboxylic acid or amide functionality. Specific examplesinclude but are not limited to maleic anhydride, methylmaleic anhydride,glutaconic anhydride, itaconic anhydride, citraconic anhydride,mesaconic anhydride, maleimide and N-methylmaleimide. Also useful aremono-ester and bis-ester derivatives of the aforementioned.

Other monomers useful in the present invention include acrylamide andderivatives such as but not limited to N-alkyl acrylamides, N-arylacrylamides and N-alkoxyalkyl acrylamides. Specific examples includeN-methyl acrylamide, N-ethyl acrylamide, N-butyl acrylamide,N,N-dimethyl acrylamide, N,N-dipropyl acrylamide,N-(1,1,2-trimethylpropyl)acrylamide, N-(1,1,3,3-tetramethylbutyl)acrylamide, N-methoxymethyl acrylamide, N-methoxyethyl acrylamide,N-methoxypropyl acrylamide, N-butoxymethyl acrylamide, N-isopropylacrylamide, N-s-butyl acrylamide, N-t-butyl acrylamide, N-cyclohexylacrylamide, N-(1,1-dimethyl-3-oxobutyl)acrylamideN-(2-carboxyethyl)acrylamide, 3-acrylamido-3-methyl butanoic acid,methylene bisacrylamide, N-(3-aminopropyl)acrylamide hydrochloride,N-(3,3-dimethylaminopropyl)acrylamide hydrochloride,N-(1-phthatamidomethyl)acrylamide, sodiumN-(1,1-dimethyl-2-sulfoethyl)acrylamide and the correspondingmethacrylamides.

Besides being derived from styrenic and acrylic monomers, the additionpolymers useful in the present invention may have functionality derivedfrom a variety of other types of monomers well known in the art ofpolymer chemistry. Such monomers include vinyl derivatives andethylenically unsaturated compounds in general. Examples of these othermonomer types include but are not limited to olefins (e.g.,dicyclopentadiene, ethylene, propylene, 1-butene, 5,5-dimethyl-1-octene,etc.); halogenated olefins (e.g., vinyl chloride, vinylidene chloride,etc.); {acute over (α)}-alkylalkenes, acrylonitriles, acroleins, vinylethers, vinyl esters, vinyl ketones, vinylidene chloride compounds,allyl compounds, and ethylenically unsaturated heterocyclic compounds.Specific examples include allyl acetate, allyl caproate, methyl vinylether, butyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinylether, chloroethyl vinyl ether, 1-methyl-2,2-dimethylpropyl vinyl ether,hydroxyethyl vinyl ether, diethylene glycolvinyl ether,dimethylaminoethyl vinyl ether, butylaminoethyl vinyl ether, benzylvinyl ether, tetrahydrofurfuryl vinyl ether, vinyl acetate, vinylpropionate, vinyl butyrate, vinyl isobutyrate, vinyl dimethylpropionate, vinyl ethyl butyrate, vinyl chloroacetate, vinyldichloroacetate, vinyl methoxyacetate, vinyl phenyl acetate, vinylacetoacetate, N-vinyl oxazolidone, N-vinylimidazole, N-vinylpyrrolidone,N-vinylcarbazole, vinyl thiophene and N-vinylethyl acetamide.

The addition polymers useful in the present invention may be derivedfrom monomers capable of absorbing UV light after polymerization.Examples of such monomers are disclosed and claimed in U.S. Pat. No.6,699,538. A variety of other types of monomers well known in the art ofpolymer chemistry can be used. Still other monomer types includemultifunctional monomers having some combination of functionalitydescribed above.

Addition polymers useful in the present invention are commonly preparedby free radical polymerization of vinyl or ethylenically unsaturatedmonomers; however, other polymerization methods such as anionicpolymerization, cationic polymerization, polyinsertion, and others wellknown in polymerization chemistry are also suitable. Synthetictechniques well known in the art of polymer chemistry include but arenot limited to emulsion polymerization, solution polymerization,suspension polymerization and dispersion polymerization.

In one embodiment the acrylic polymer is a copolymer comprising benzylmethacrylate and methacrylic acid. In another embodiment, the additionpolymer is a styrene-acrylic copolymer comprising a mixture of vinyl orunsaturated monomers, including at least one styrenic monomer and atleast one acrylic monomer, at least one of which monomers has an acid oracid-providing group.

The following commercially available styrene-acrylic polymers may beemployed in the composition of the invention, for example,styrene-acrylic polymer having acid number 240, sold as Joncryl® 70 fromS.C. Johnson Co. (Wisconsin, USA); a styrene-acrylic polymer having acidnumber 230 sold as TruDot™ IJ-4655 from MeadWestvaco Corp. (Stanford,Conn., USA); a styrene-acrylic polymer having acid number 215 sold asJoncryl® 59 from S.C. Johnson Co.; a styrene-acrylic polymer having acidnumber 215 sold as Joncryl® 57 from S.C. Johnson Co.; a styrene-acrylicpolymer having acid number 213 sold as Joncryl® 63 from S.C. JohnsonCo.; a styrene-acrylic polymer having acid number 172 sold as TruDot™IJ-4680 from MeadWestvaco Corp.; an acrylic resin having acid number 160sold as Vancryl® 68S from Air Products and Chemicals, Inc. (Allentown,Pa.).

Prior to use, preferably the acid groups of the at least two differentpolymers are partially or completely neutralized. It is preferred that50% or more of the acid groups of each polymer are neutralized. It ismore preferred that 70% or more of the acid groups of each polymer areneutralized. The acid groups may be neutralized with any suitable base,examples of which include inorganic or organic bases such as alkalimetal hydroxides, ammonia, mono-, di- and trialkyl- or aryl amines,nitrogen-containing heterocycles; and tetraalkyl- or aryl amines and thelike. Specific examples of bases include sodium hydroxide, potassiumhydroxide, lithium hydroxide, ammonia, triethylamine, triethanolamine,diethanolamine, 4-ethylmorpholine or dimethylethanolamine. The identityand amount of base used is dependent on the desirable viscosity,jettability through printhead type and print durability and otherproperties delivered by the ink composition of the present invention. Ina preferred embodiment of the invention, an inorganic base such assodium hydroxide or potassium hydroxide is used.

The polymers employed in the present invention may be eitherwater-soluble, or water-dispersible. By the term “water-soluble” ismeant herein that the polymer is dissolved in water such that scatteringis not observed when a dilute solution of the polymer is analyzed usingdynamic light scattering or any other technique well known in the art ofparticle analysis. By the term “water-dispersible” is meant herein thatthe polymer exists in the form of particles in water, the particlesbeing dispersed or suspended and often stabilized against flocculationand settling by the use of dispersing agents. In contrast to awater-soluble polymer, a dilute solution of a water-dispersible polymerexhibits scattering when analyzed using dynamic light scattering or anyother technique well known in the art of particle analysis.

The ratio of the first (preferably a condensation polymer) polymer tothe second (preferably an addition polymer) polymer is preferably 1:2 to4:1. Both may be present in any amount as long as they meet the weightaverage acid number requirement. Factors that must be considered includedurability, resolution and drop size capacity of the printhead, printspeed, application method (pre during or post colored inks) maskingpattern, etc., as well as the properties of the ink and recordingelement used to form the printed image. In general, the first polymer ispresent in the composition in an amount of up to 20% by weight of thecomposition. The first polymer is preferably present in an amount of upto 10% by weight of the composition, and more preferably up to 5% byweight of the composition. In general, the second polymer is present inthe composition in an amount of up to 20% by weight of the composition,preferably in an amount of up to 10% by weight of the composition, andmore preferably up to 5% by weight of the composition. Generally bothpolymers are present in at least the amount 0.1% by weight.

The ink composition may also comprise only the polyurethane polymer thathas an acid number of 60 to 100 and a molecular weight of greater than10,000 or the acrylic polymer that has an acid number greater than 180and a molecular weight of less than 18,000. These polymers may be thoseas described in detail above.

Particularly when used as a colorless coating in an overcoat format thepolymers are present in the ink composition in an amount required togive a protective overcoat of desired water and stain resistance afterthe overcoat composition has been printed and dried. By the term “stainresistance” is meant herein that, after printing, the imaged recordingelement does not imbibe water or has a protective overcoat that preventsor minimizes water-based stains from discoloring the imaged side of theimaged-recording element. Furthermore, the overcoat thickness, or drylaydown of polymer, is not particularly limited, and is determined notonly by the inherent capacity of that polymer to function as aprotective overcoat, but also by numerous other factors as discussedabove. The overcoat thickness is not particularly limited, but ispreferably up to about 4 microns, and more preferably up to about 2microns.

The colored ink or the anionic polymer ink can additionally comprisecharge compatible charged protective filler particles activated onadmixing the inks. Examples include: a first ink having an anionicpolymer and anionic charged protective filler to be mixed with a secondink having a cationic charged pigment; a first ink having anionicpolymer to be mixed with a second ink having a cationic charged pigmentand a cationic charged protective filler particle; and a first inkhaving an anionic polymer and anionic charged protective filler to bemixed with a second ink having a cationic charged pigment and a cationiccharged protective filler particle.

The exact choice of ink components will depend upon the specificapplication and performance requirements of the printhead from whichthey are jetted and the media type to be printed upon. Thermal andpiezoelectric drop-on-demand printheads and continuous printheads eachrequire ink compositions with a different set of physical properties inorder to achieve reliable and accurate jetting of the ink, as is wellknown in the art of inkjet printing. Acceptable surface tensions aretypically no greater than 60 dynes/cm, and preferably in the range of 20dynes/cm to 45 dynes/cm.

When the composition is a substantially colorless composition it may bethe same or different from the formulations of the colored inks that areused in that particular printhead or printing system. The inkcompositions useful in the invention may include humectants and/orco-solvents in order to prevent the ink composition from drying out orcrusting in the nozzles of the printhead, aid solubility of thecomponents in the ink composition, or facilitate penetration of the inkcomposition into the recording element after printing.

Representative examples of humectants and co-solvents used inaqueous-based ink compositions include (1) alcohols, such as methylalcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butylalcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfurylalcohol, and tetrahydrofuryl alcohol; (2) polyhydric alcohols, such asethylene glycol, diethylene glycol, triethylene glycol, tetraethyleneglycol, propylene glycol, polyethylene glycol, glycerol,2-methyl-2,4-pentanediol, 1,2,6-hexanetriol,2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,5 pentanediol,1,2-hexanediol, and thioglycol; (3) lower mono- and di-alkyl ethersderived from the polyhydric alcohols; (4) nitrogen-containing compoundssuch as urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, and1,3-dimethyl-2-imidazolidinone; and (5) sulfur-containing compounds suchas 2,2′-thiodiethanol. Typical aqueous-based ink compositions useful inthe invention may contain, for example, the following components basedon the total weight of the ink: water 20-95%, humectant(s) 5-70%, andco-solvent(s) 2-20%.

Other components present in the colorless ink compositions of theinvention include surfactants, defoamers, biocides, buffering agents,conductivity enhancing agents, anti-kogation agents, drying agents,waterfast agents, chelating agents, light stabilizers, or ozonestabilizers. When the ink is a substantially colorless ink or overcoatcomposition it may be colored with very small amounts of colorants inorder to impart a desired hue to any or all of the printed image, or insome cases, to correct the color balance of a printed image. Usefulcolorants include pigments, dyes, polymeric dyes, loaded-dye/atexparticles, or combinations thereof, and many of these types of colorantsare well known in the art of ink jet inks. In general, colorants may beused in an amount of up to about 0.2% by weight of the composition.

The ink jet ink composition is applied to a printed image using an inkjet printhead. Any type of printhead may be used including, but notlimited to, drop-on-demand printheads which utilize piezoelectrictransducers or thermal bubble formation, or continuous printheads whichutilize electrostatic charging devices and deflector plates. Theinvention is particularly suitable for use with a thermal printhead.Examples of printheads useful in the invention include those used inCanon USA, Inc., Hewlett-Packard Co., and Epson America Inc. desktop andwide-format ink jet printers, and in printing systems described in U.S.2004/0100542 A1; U.S. 2003/0117465 A1; U.S. 2003/0043223 A1; U.S. Pat.No. 6,079,821; U.S. Pat. No. 6,450,619 B1; U.S. Pat. No. 6,217,163 B1;U.S. 2004/0032473 A1, U.S. 2003/0189626 A1, or U.S. 2004/0017406 A1. Theprinthead used in the invention may be part of any type of conventionalinkjet printing system that deposits one or more inks or fluids onto anrecording element.

When the composition is a substantially colorless composition theprinthead containing the substantially colorless composition may bepositioned in any one of the printhead ports intended for use withprintheads containing colored inks, or it may be positioned in aprinthead port that is intended for use with a colorless ink asdescribed in the above references. The printhead containing thesubstantially colorless composition may be positioned on the samecarriage assembly as the one used for colored inks, or it may be on aseparate carriage assembly.

The ink compositions of the invention can be applied to variousrecording elements well known in the art of ink jet printing includingboth porous and swellable types, and either may be used to generate theprinted image. Representative examples of such recording elements aredisclosed in U.S. Pat. Nos. 6,045,917; 5,605,750; 5,723,211; 5,789,070and EP 813 978 A1. In a preferred embodiment of the invention, porousrecording elements are employed because they dry quickly. In anotherpreferred embodiment of the invention, porous recording elements havinghigh gloss are employed because they render photographic quality printedimages. In one preferred embodiment the ink jet receiver is plain paper.

When the ink composition is substantially colorless it is preferred thatthe ink be printed in a predetermined pattern or in image specificlevels in various portions of the printed image rather than beingapplied as a uniform overcoating. This type of approach permitsselective application of the substantially colorless ink to areas of theimage where environmental protection or optical improvements arerequired and can decrease the total volume of liquid applied to themedia resulting in higher image quality, reduced media cockle and lowermedia ink capacity media requirements. U.S. Pat. No. 5,515,479 teachesone such method for limiting the volume of colored ink used to print animage but it is obvious to one skilled in the art that similarapproaches can be utilized for the application of substantiallycolorless materials.

This invention also comprises a method of printing an ink jet imagecomprising separately applying to an ink jet receiver a colored ink anda substantially colorless ink, wherein the colored ink comprises acationic coloring agent and the colorless ink comprises an anionicpolymer or oligomer, and wherein the inks are applied in substantiallyan overlaying manner. The inks are as described in detail above. In oneembodiment the inks are applied simultaneously in substantially anoverlaying manner. In another embodiment the first ink is applied andsubsequently the second ink is applied in an overlaying manner; or thesecond ink is applied and subsequently the first ink is applied in anoverlaying manner. By overlying manner, it is meant that the two inksare applied to the media at closely enough to be in reactive associationthereby enabling electrostatic cross reaction between the distinctlycharged particles in the two distinct inks. In a preferred embodimenteach of the first and second ink would have a dedicated delivery channelto avoid having the oppositely charged materials in the two inksinteract until they come in reactive association on the intended media.The colorless ink may be applied either in the same pass as the one thatjets the colored inks, or in a different pass.

In a preferred embodiment the printer comprises a thermal printhead. Inanother preferred embodiment, the ink jet recording element is a plainpaper.

The following example is provided to illustrate, but not to limit, theinvention.

EXAMPLES Polymer Characterization

Weight Average Molecular Weight M_(w)

Polymer samples were analyzed by size-exclusion chromatography usingdifferential viscometry detection and a universal calibration curve asdescribed in: T. H. Mourey and T. G. Bryan, Journal of Chromatography A,964 (2002) 169-178. The eluent employed was1,1,1,3,3,3-hexafluoroisopropanol containing 0.01 M tetraethylammoniumnitrate. Columns used were two 7.5 mm×300 mm PLGel Mixed-C columns,available from Polymer Labs, and both columns were thermostated at 45°C. The absolute molecular weight distribution was calculated fromviscosity data, and a universal calibration curve constructed fromnarrow-molecular weight poly(methylmethacrylate) standards between 620(log M=2.79) and 1,450,000 (log M=6.16). Any portion of a polymerdistribution appearing beyond the calibration range of the column setwas not used for quantitative purposes. The ordinate “W_(n)(logM)” wasproportional to the weight fraction of the polymer at a given molecularweight on a logarithmic scale. Weight average molecular weight (M_(w))and number average molecular weight (M_(n)) in HFIP at 45° C. arereported.

Calculated Acid Number, AN

Acid number is defined as the amount of KOH (in mg) required toneutralize 1 g of polymer. The acid number for each of the polymers wascalculated using the amount of the monomer having a carboxylic acidgroup, the total amount of the monomers used in the synthesis of thepolymer, and the molecular weight of the base used to neutralize thepolymer according to the following equation:

${AN} = {( \frac{{amountof}\mspace{14mu} B\; H\; M\; P\;{A({mol})}}{{totalamountof}\mspace{14mu}{{monomers}(g)}} )( {{MW}\mspace{14mu}{of}\mspace{14mu}{{base}( \frac{g}{mol} )}} )(1000)}$

For example, referring to Polyurethane 1 of the Invention, PU-1, that isdescribed below, the acid number was calculated as follows: the amountof the monomer having a carboxylic acid group was 0.432 mol, the totalamount of the monomers used in the synthesis of the PU-1 was(136+57.9+107.8) g=301.7 g, and the molecular weight of KOH is 56 g/mol:

${AN} = {{( \frac{0.432\mspace{14mu}{mol}}{301.7\mspace{14mu} g} )( {56\frac{g}{mol}} )(1000)} = 80}$Weight average acid number of polymer mixture=(Wt % of a firstpolymer×AN of a first polymer)+(wt % of a second polymer×AN of a secondpolymer)+etc, wherein the sum of wt % of all polymers equals 100%.Preparation of PolyurethanesPolyurethane 1 useful in the Invention, PU-1

In a 1-liter round bottom flask equipped with thermometer, stirrer,water condenser and a vacuum outlet was placed 136 g (0.068 moles) ofpoly(hexamethylene carbonate) diol, avg. M_(n)=2000 (Aldrich 46, 116-4).It was dewatered under vacuum at 100° C. The vacuum was released and thefollowing were added at 40° C. while stirring: 57.9 g (0.432 moles)2,2-bis(hydroxymethyl) propionic acid (BHMPA), 160 g tetrahydrofuran(THF), and 1 mL of stannous octoate (catalyst). The temperature wasadjusted to 68° C., and when a homogeneous solution was obtained, 107.8g (0.485 moles) of isophorone diisocyanate (IPDI) was slowly added,followed by 10 mL THF. The temperature was raised to 72 C and maintainedfor about 16 hours to complete the reaction, resulting in anintermediate containing less than 3% of free IPDI. The free IPDI contentwas monitored by IR spectroscopy of the absorption peak at 2240 wavenumber.

The reaction mixture was diluted with 200 mL THF, and neutralized with53.86 g of 45 wt. % KOH solution to achieve 100% stoichiometricionization based on the amount of BHMPA. Under high shear, 900 mL ofdistilled water was added and THF was subsequently removed by heatingunder vacuum to give an aqueous solution of PU-1 at 27.51 wt. % solids.The molecular weights of PU-1 were M_(w)=18,800 and M_(n)=8440; and theAN=80.

Polyurethane 2 Useful in the Invention, PU-2

The procedure was repeated with the following modifications: 140 g(0.070 moles) of poly(hexamethylene carbonate) diol; 57.7 g (0.430moles) BHMPA; 106.7 g (0.480 moles) IPDI; neutralized with 53.62 g of 45wt. % KOH solution. The final solution was 32.34 wt. % solids. Themolecular weights of PU-5 were M_(w)=12,800 and M_(n)=5620; and theAN=79.

Styrene-acrylic Polymer Useful in the Invention

TruDot™ IJ-4655, commercially available from Westvaco Corp., has an acidnumber of 230 quoted from Wastvaco. A 25% by weight of aqueous solutionwas prepared by mixing polymer resin, potassium hydroxide and water andstirred at 60 C for 8 hours. Potassium hydroxide was added at 95 mole %based on its acid number. The molecular weight of SA-1 was Mw=16700 andMn=5670.

Acrylic Polymer Useful in the Invention

100 g of diethylene glycol (DEG) and 0.25 g of2,2′-azobisisobutyronitrile (AIBN) were charged to a 1-liter, three-neckround-bottom flask equipped with a mechanical stirrer and nitrogeninlet. The resulting solution was purged with nitrogen for 20 minutesand heated to 150 degrees Centigrade in a constant temperature bath. Ina separate container, 100 g of DEG, 0.25 g of AIBN, 33.5 g of benzylmethacrylate (BM), and 16.5 g of methacrylic acid (MA) were combined,mixed well, and then added to the first solution over 2 hours.Polymerization was continued for 3 hours. The temperature was reduced to65-70 degrees Centigrade, and 1 mL each of t-butyl hydroperoxide (10weight percent) and sodium formaldehyde bisulfite (10 weight percent)were then added. The resulting polymer was isolated and a 20 wt. %aqueous solution prepared by neutralizing the polymer to 65-70 wt. %with potassium hydroxide.

The resulting random copolymer of BM/MA in a 67/33-weight ratio wasfound to have a number average molecular weight of 4960 and a weightaverage molecular weight of 7580. The calculated acid number is 215.

Example 1 Preparation of Ink-jet Ink Samples 1 Through 5

Ink-jet Ink 1 (anionic polymer clear ink) was prepared by mixing 4.4%Trudot IJ4655 (a styrene—acrylic acid co-polymer) with 5% diethyleneglycol, 2.5% glycerol, and 0.5% Surfynol-465 with the balance water atpH ˜8.2.

Ink-jet Ink 2 (anionic polymer clear ink) was prepared by mixing 4.4%Trudot IJ4655 with 5% diethylene glycol, 2.5% glycerol, and 0.5%Strodex-PK90 with the balance water at pH 8.2.

Ink-jet Ink 3 (anionic polymer clear ink) was prepared by mixing Trudot4.4% IJ4655 with 5% diethylene glycol, 2.5% glycerol, 2.5% diethyleneglycol mono-butyl ether and 0.5% Surfynol-465 with the balance water atpH ˜8.2.

Ink-jet Ink 4 (anionic self-dispersed colored pigment ink) was preparedby mixing about 4% of an anionic self-dispersed carbon black (from a 15%dispersion of carboxylate derivatized carbon black (PK7) preparedaccording to Johnson and Belmont, U.S. Pat. No. 5,922,118 an averageparticle size of about 130 nm), with 12% diethylene glycol, 0.5% StrodexPK-90 surfactant and 0.06% tri ethanol amine with the balance water atpH ˜8.3.

Ink-jet Ink 5 (cationic self dispersed colored pigment ink) was preparedby mixing about 4% of a cationic self-dispersed carbon black (from a 10%dispersion of polyethyleneimine derivatized carbon black (PK7) preparedaccording to Palumbo and Lando in WO 01/51566 A1 at an average particlesize of about 130 nm), with 12% diethylene glycol, 0.1% Strodex PK-90surfactant with the balance water at pH ˜5.

Example 2 Application and Evaluation of Images Formed by Inks 1 Through5 on a Variety of Plain Papers

Inks 1 to 5 (carbon black inks and clear polymeric inks) were appliedsingly and in combination using a thermal ink jet apparatus (Canon i960)to a variety of commercially available general purpose and ink-jetdesigned plain papers. Both the formed density and the uniformity of theformed density deposits were examined. The uniformity of the formeddeposits can be influenced by the appearance of paper fibers that arenot colored by the applied inks or ink combinations. The results arereported in Table 1, below. This table recites formed density on severalplain papers, the average density across the paper set and the densitycoefficient of variation (COV) across the paper set as a function of theapplied inks. Needless to say, high average density with low density COVis a desired outcome.

TABLE I Multipurpose Multipurpose InkJet plain Multipurpose InkJet plainAverage Density Density COV Office Paper 1 Office Paper 2 paper 1 OfficePaper 3 paper 2 Across Media across media 0.07 0.08 0.06 0.06 0.05 0.0617.8 Anionic polymer Ink 1 0.07 0.08 0.06 0.06 0.05 0.06 17.8 Anionicpigment Ink 4 1.25 1.16 1.30 1.08 1.31 1.22 8.1 Inks 1 and 4 0.92 0.920.94 0.87 1.03 0.94 6.3 Anionic polymer Ink 2 0.08 0.08 0.06 0.06 0.050.07 20.3 Anionic pigment Ink 4 1.27 1.19 1.29 1.10 1.42 1.25 9.5 Inks 2and 4 0.92 0.97 0.97 0.87 1.10 0.97 8.9 Anionic polymer Ink 3 0.08 0.080.06 0.07 0.05 0.07 19.2 Anionic pigment Ink 4 1.24 1.15 1.24 1.04 1.401.21 10.9 Inks 3 and 4 0.86 0.94 0.95 0.86 1.06 0.93 8.8 Anionic polymerInk 1 0.07 0.07 0.06 0.07 0.05 0.06 14.0 Cationic pigment Ink 5 1.081.08 1.07 1.15 1.11 1.10 3.0 Inks 1 and 5 1.40 1.36 1.45 1.40 1.43 INV1.41 2.4 Anionic polymer Ink 2 0.07 0.08 0.06 0.07 0.05 0.07 17.3Cationic pigment Ink 5 1.08 1.11 1.11 1.15 1.10 1.11 2.3 Inks 2 and 51.46 1.46 1.49 1.47 1.48 INV 1.47 0.9 Anionic polymer Ink 3 0.08 0.080.06 0.07 0.05 0.07 19.2 Cationic pigment Ink 5 1.09 1.08 1.09 1.16 1.081.10 3.1 Inks 3 and 5 1.49 1.45 1.51 1.46 1.51 INV 1.48 1.9

As is readily apparent, the presence of the cationic pigment incombination with an anionic polymeric material applied from distinctheads to the same area provides for the improved density across a widevariety of media and further provides the smallest variation in formeddensity between the various media, thus improving the consumer ink-jetexperience. Notice further that the combination of an anionic pigment incombination with an anionic polymer degrades the density performance ofthe anionic pigment. So, the ability to employ the anionic polymer forits water-fastness and image stability roles is compromised except whenemployed in combination with a cationic pigment.

Example 3 Preparation of Ink-jet Ink Samples 6 Through 10

Ink-jet ink 6 (anionic self-dispersed colored pigment ink) was preparedby mixing about 4% of an anionic self-dispersed carbon black (from a 15%dispersion of carboxylate derivatized carbon black (PK7) preparedaccording to Johnson and Belmont, U.S. Pat. No. 5,922,118 an averageparticle size of about 130 nm), with 12% polyethylene glycol (Mw ˜600daltons), 3% 2-pyrrolidinone, 0.5% Surfynol-465 surfactant with thebalance water at pH ˜8.3.

Ink-jet ink 7 (anionic conventionally dispersed) was prepared by mixingabout 4% of anionic surfactant stabilized carbon black (from a 12%dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersed carbonblack (PK7) micro-milled according to Bishop and Czekai, U.S. Pat. No.5,679,138 to an average particle size of about 50 nm), with 12%Polyethylene Glycol (Mw ˜300), 3% 2-pyrrolidinone, 0.1% Surfynol-465with the balance water at pH ˜8.3.

Ink-jet ink 8 (cationic conventionally dispersed) was prepared by mixingabout 4% of a cationic surfactant stabilized cyan pigment (from amicro-milled dispersion of Cetyl-trimethyl ammonium bromide [CTAB]dispersed cyan copper phthalocyanine pigment (See Wang et al EK Docket88567 not yet filed) dispersed at ca 4:1 with 12% Polyethylene Glycol(Mn ˜400), 3% 2-pyrrolidinone, 0.1% Surfynol-465 with the balance water.

Ink-jet ink 9 (cationic conventionally dispersed) was prepared by mixingabout 4% of a cationic surfactant stabilized cyan pigment (from amicro-milled dispersion of Cetyl-trimethyl ammonium bromide [CTAB]dispersed cyan copper phthalocyanine pigment (See Wang et al EK Docket88567 not yet filed) dispersed at ca 2:1 with 12% Polyethylene Glycol(Mn ˜400), 3% 2-pyrrolidinone, 0.1% Surfynol-465 with the balance water.

Inkjet Ink 10 (cationic self dispersed) was prepared by mixing about 4%of a cationic self-dispersed carbon black (from a 10% dispersion ofpolyethyleneimine derivatized carbon black (PK7) prepared according toPalumbo and Lando in WO 01/51566 A1 at an average particle size of about50 nm), with 12% Polyethylene Glycol (Mn ˜400), 3% 2-pyrrolidinone, 0.1%Surfynol-465 surfactant with the balance water at pH 5.

Example 4 Application and Evaluation of Images Formed by Inks 6 Through10 on a Variety of Plain Papers

Inks 6 to 10 (text black inks and polymeric clear inks) were appliedsingly and in combination using a thermal ink jet apparatus (Canon i960)to a variety of commercially available general purpose and ink-jetdesigned plain papers. Both the formed density and the uniformity of theformed density deposits were examined. The uniformity of the formeddeposits can be influenced by the appearance of paper fibers that arenot colored by the applied inks or ink combinations. The results arereported in Table II, below. This table recites formed density onseveral plain papers, the average density across the paper set and thedensity coefficient of variation (COV) across the paper set as afunction of the applied inks. Needless to say, high average density withlow density COV is a desired outcome.

TABLE II Multipurpose Multipurpose InkJet plain Average Density DensityCOV Office Paper 1 Office Paper 3 paper 1 Across Papers across PapersDmin 0.08 0.07 0.07 0.07 9.5 Anionic pigment Ink 6 1.33 1.32 1.34 1.330.8 Anionic polymer Ink 3 0.09 0.07 0.08 0.08 10.2 Inks 3 and 6 0.930.96 0.89 0.92 4.1 Anionic pigment Ink 7 1.09 1.09 1.08 1.09 0.6 Anionicpolymer Ink 3 0.09 0.07 0.08 0.08 10.2 Inks 3 and 7 0.83 0.91 0.86 0.864.5 Cationic pigment Ink 8 1.11 1.07 1.03 1.07 4.1 Anionic polymer Ink 30.09 0.08 0.09 0.09 8.0 Inks 3 and 8 1.11 1.15 1.10 INV 1.12 2.5Cationic pigment Ink 9 0.90 0.82 0.79 0.83 6.6 Anionic polymer Ink 30.11 0.08 0.12 0.10 16.2 Inks 3 and 9 1.00 0.91 0.88 INV 0.93 6.8Cationic pigment Ink 10 1.13 1.01 1.11 1.08 5.6 Anionic polymer Ink 30.09 0.08 0.08 0.08 6.9 Inks 3 and 10 1.22 1.26 1.26 INV 1.24 2.0

As is readily apparent, the presence of the cationic pigment incombination with an anionic polymeric material applied from distinctheads to the same area provides for the improved density across a widevariety of media and further provides the smallest variation in formeddensity between the various media thus improving the consumer ink-jetexperience. Notice further that the combination of an anionic pigment incombination with an anionic polymer degrades the density performance ofthe anionic pigment. So, the ability to employ the anionic polymer forits water-fastness and image stability roles is compromised except whenemployed in combination with a cationic pigment.

Example 5 Preparation of Ink-jet Ink Samples 11 Through 23

Inkjet ink 11 (anionic polymer clear ink) was prepared by mixing 0.8%Trudot IJ4655, 2.4% bezylmethacrylate—acrylic acid copolymer, with 12.5%diethylene glycol, 5% glycerol and 0.5% Strodex PK-90 with the balancewater at pH ˜8.2.

Ink-jet ink 12 (cationic conventionally dispersed) was prepared bymixing about 2.5% of a cationic surfactant stabilized cyan pigment (froma micro-milled dispersion of Cetyl-trimethyl ammonium bromide [CTAB]dispersed cyan copper phthalocyanine pigment, with 15% PolyethyleneGlycol (Mn ˜300), 6% 2-pyrrolidinone, 0.2% Surfynol-465 with the balancewater.

Ink-jet ink 13 (cationic conventionally dispersed) was prepared bymixing about 3% of a cationic surfactant stabilized magenta pigment(from a micro-milled dispersion of Cetyl-trimethyl ammonium bromide[CTAB] dispersed magenta pigment PR122 , with 15% Polyethylene Glycol(Mn ˜300), 6% 2-pyrrolidinone, 0.2% Surfynol-465 with the balance water.

Ink-jet ink 14 (cationic conventionally dispersed) was prepared bymixing about 3.2% of a cationic surfactant stabilized yellow pigment(from a micro-milled dispersion of Cetyl-trimethyl ammonium bromide[CTAB] dispersed yellow pigment PY74 , with 15% Polyethylene Glycol (Mn˜300), 6% 2-pyrrolidinone, 0.2% Surfynol-465 with the balance water.

Ink-jet ink 15 (cationic conventionally dispersed) was prepared bymixing about 3.2% of a cationic surfactant stabilized yellow pigment(from a micro-milled dispersion of Cetyl-trimethyl ammonium bromide[CTAB] dispersed yellow pigment PY155 , with 15% Polyethylene Glycol (Mn˜300), 6% 2-pyrrolidinone, 0.2% Surfynol-465 with the balance water.

Ink-jet ink 16 (cationic conventionally dispersed) was prepared bymixing about 2.2% of a cationic surfactant stabilized cyan pigment (froma micro-milled dispersion of Cetyl-trimethyl ammonium bromide [CTAB]dispersed cyan copper phthalocyanine pigment with 15% PolyethyleneGlycol (Mn ˜300), 6% 2-pyrrolidinone, 0.2% Surfynol-465 with the balancewater.

Ink-jet Ink 17 (anionic conventionally dispersed) was prepared by mixingabout 2.5% of anionic surfactant stabilized cyan pigment (from a ca. 10%dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersed cyanpigment PB15:3 micro-milled according to Bishop and Czekai, U.S. Pat.No. 5,679,138, with 15% Polyethylene Glycol (Mn ˜300), 6%2-pyrrolidinone, 0.2% Surfynol-465 with the balance water at pH ˜8.3.

Ink-jet ink 18 (cationic polymeric dispersed) was prepared by mixingabout 2.2% of an cationic polymer stabilized carbon black (from a 9%dispersion of carbon black (PK7) micro milled to average particle sizeof about 50 nm, in the presence of a N,N,N-trimethylethanolammoniummethyacrylate-benzyl methacrylate copolymer, with 15% PolyethyleneGlycol (Mn ˜400), 9% 2-pyrrolidinone, 0.2% Surfynol-465 with the balancewater at pH ˜5.

Ink-jet ink 19 (anionic self dispersed) was prepared by mixing about 4%of an anionic self-dispersed carbon black (from a 15% dispersion ofcarboxylate derivatized carbon black (PK7) prepared according to Johnsonand Belmont, U.S. Pat. No. 5,922,118 an average particle size of about130 nm), with 25% diethylene glycol, 0.1% Surfynol-465 surfactant and0.1% triethanol amine with the balance water at pH ˜8.3.

Ink-jet Ink 20 (anionic conventionally dispersed) was prepared by mixingabout 2.2% of anionic surfactant stabilized carbon black (from a 12%dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersed carbonblack (PK7) micro-milled according to Bishop and Czekai, U.S. Pat. No.5,679,138 to an average particle size of about 50 nm), with 25%diethylene glycol, 1% IJ4655 (Trudot), 0.5% Surfynol-465 surfactant and0.5% triethanol amine with the balance water at pH ˜8.3.

Ink-jet Ink 21 (anionic conventionally dispersed) was prepared by mixingabout 2.5% of anionic surfactant stabilized magenta pigment (from a ca.10% dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersedcyan pigment PB 15:3 micro-milled according to Bishop and Czekai, U.S.Pat. No. 5,679,138, with 6.8% diethylene glycol, 3% glycerol, 2.5%diethylene glycol mono-butyl ether, 1.7% Trudot and 0.1% Surfynol-465with the balance water at pH ˜8.3.

Ink-jet Ink 22 (anionic conventionally dispersed) was prepared by mixingabout 3% of anionic surfactant stabilized magenta pigment (from a ca.10% dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersedmagenta pigment PR122 micro-milled according to Bishop and Czekai, U.S.Pat. No. 5,679,138, with 18% diethylene glycol, 5% glycerol, 1.2% Trudotand 0.5% Surfynol-465 with the balance water at pH ˜8.3.

Ink-jet Ink 23 (anionic conventionally dispersed) was prepared by mixingabout 3.2% of anionic surfactant stabilized yellow pigment (from a ca10% dispersion of OMT [potassium N-methyl-N-oleoyl taurate] dispersedyellow pigment PY155 micro-milled according to Bishop and Czekai, U.S.Pat. No. 5,679,138, with 5% diethylene glycol, 10% glycerol, 1.6% Trudotand 0.5% Surfynol-465 with the balance water at pH ˜8.3.

Example 6 Application and Evaluation of Images Formed by Inks 6 Through10 on a Variety of Plain Papers

Inks 11 to 23 (colored pigment inks and polymeric clear inks) wereapplied singly and in combination using a thermal ink jet apparatus(Canon i960) to a variety of commercially available general purpose andink-jet designed plain papers. Both the formed density and theuniformity of the formed density deposits were examined. Densities wereread as Status A on peak densities under D55 illumination. Theuniformity of the formed deposits can be influenced by the appearance ofpaper fibers that are not colored by the applied inks or inkcombinations. The results are reported in Table III, below. This tablerecites formed density on several plain papers, the average densityacross the paper set and the density coefficient of variation (COV)across the paper set as a function of the applied inks. Needless to say,high average density with low density COV is a desired outcome.

TABLE III Multipurpose Multipurpose InkJet plain Average Density DensityCOV Office Paper 1 Office Paper 3 paper 1 Across Papers across PapersAnionic polymer Ink 11 0.12 0.11 0.10 0.11 8.4 Paper Dmin 0.12 0.11 0.090.11 14.7 Cationic Pigment Ink 12 0.94 0.92 0.85 0.90 4.8 Both Inks 11and 12 1.09 1.06 1.03 INV 1.06 2.8 Cationic Pigment Ink 14 0.93 0.950.86 0.91 5.2 Both Inks 11 and 14 1.06 1.05 1.02 INV 1.04 2.2 CationicPigment Ink 15 0.86 0.86 0.79 0.84 5.1 Both Inks 11 and 15 1.01 1.011.04 INV 1.02 1.7 Cationic Pigment Ink 16 1.21 1.12 0.97 1.10 11.2 BothInks 11 and 15 1.33 1.31 1.27 INV 1.30 2.3 Anionic Pigment Ink 17 0.960.94 0.85 0.92 6.3 Both Inks 11 and 17 0.78 0.82 0.76 0.79 4.1 AnionicPigment Ink 19 1.31 1.48 1.44 1.41 6.4 Both Inks 11 and 19 0.91 0.920.96 0.93 2.9 Anionic Pigment Ink 20 0.82 0.86 0.80 0.82 3.9 Both Inks11 and 20 0.74 0.80 0.71 0.75 5.8 Anionic Pigment Ink 21 0.83 0.88 0.860.86 2.8 Both Inks 11 and 21 0.82 0.85 0.78 0.82 4.2 Anionic Pigment Ink22 0.80 0.82 0.80 0.80 1.5 Both Inks 11 and 22 0.71 0.75 0.71 0.72 3.1Anionic Pigment Ink 23 0.81 0.81 0.77 0.80 2.6 Both Inks 11 and 23 0.760.76 0.71 0.75 3.8

As is readily apparent, the presence of the cationic pigment incombination with an anionic polymeric material applied from distinctheads to the same area provides for the improved density across a widevariety of media and further provides the smallest variation in formeddensity between the various media thus improving the consumer inkjetexperience. Notice further that the combination of an anionic pigment incombination with an anionic polymer degrades the density performance ofthe anionic pigment. So, the ability to employ the anionic polymer forits water-fastness and image stability roles is compromised except whenemployed in combination with a cationic pigment.

Example 7 Layout for Printing of Color and Gray Scale Images on aVariety of Media

In an ink-jet printer system accommodating six delivery systems, theindividual delivery systems are each charged with Inks employing eitheranionic or cationic materials according to the following scheme:

-   -   Text-Black delivery system (Kt)—cationic black colorant having        optional cationic filler    -   Photo-Black delivery system (Kp)—anionic black colorant having        optional anionic filler particles    -   Cyan delivery system (C)—anionic cyan colorant having optional        anionic filler particles    -   Magenta delivery system (M)—anionic magenta colorant having        optional anionic filler particles    -   Yellow delivery system (Y)—anionic yellow colorant having        optional anionic filler particles    -   Protective component delivery system (P)—anionic polymeric        protective binder

The printer head driver will deliver distinct combinations of these inksdepending both on the color appropriate for the desired image or textand on user input as to plain paper v photo-paper choice.

-   Black on plain paper—system delivers Kt & P-   Black on photo paper—system delivers Kp & P-   Cyan, Magenta or Yellow on plain or photo paper—system delivers C,    M, or Y & P-   Process Black on plain paper—system delivers C, M, Y, Kt & P-   Process Black on photo paper—system delivers C, M, Y, Kp & P

Example 8 Layout for Printing of Color and Gray Scale Images on aVariety of Media

In an ink-jet printer system accommodating five delivery systems, theindividual delivery systems are each charged with Inks employing eitheranionic or cationic materials according to the following scheme:

-   -   Text-Black delivery system (Kt)—cationic black colorant    -   Cyan delivery system (C)—cationic cyan colorant having optional        cationic filler particles    -   Magenta delivery system (M)—cationic magenta colorant having        optional cationic filler particles    -   Yellow delivery system (Y)—cationic yellow colorant having        optional cationic filler particles    -   Protective component delivery system (Pa)—anionic polymeric        protective binder having optional anionic filler particles

The printer head driver will deliver distinct combinations of these inksdepending both on the color appropriate for the desired image or textCyan, Magenta, Yellow or Black—system delivers C, M, Y and/or Kt & Pa

Example 9 Layout for Printing of Color and Gray Scale Images on aVariety of Media

In an ink-jet printer system accommodating nine delivery systems, theindividual delivery systems are each charged with Inks employing eitheranionic or cationic materials according to the following scheme:

-   -   Text-Black delivery system (Kt)—cationic black colorant having        optional cationic filler    -   Photo-Black delivery system (Kp)—anionic black colorant having        optional anionic filler particles    -   Photo-Cyan delivery system (C)— anionic cyan colorant having        optional anionic filler particles    -   Photo-Magenta delivery system (M)—anionic magenta colorant        having optional anionic filler particles    -   Photo-Yellow delivery system (Y)—anionic yellow colorant having        optional anionic filler particles    -   Protective component delivery system (P)—anionic polymeric        protective binder having optional anionic filler particles    -   Text Cyan delivery system (tC)—cationic cyan colorant having        optional cationic filler particles    -   Text-Magenta delivery system (tM)—cationic magenta colorant        having optional cationic filler particles    -   Text-Yellow delivery system (tY)—cationic yellow colorant having        optional cationic filler particles

The printer head driver will deliver distinct combinations of these inksdepending both on the color appropriate for the desired image or textand on user or machine sensor input as to plain paper v photo-paperchoice.

Cyan, Magenta, Yellow or Black on plain paper—system delivers Kt, tC, tMand/or tY & P

Cyan, Magenta, Yellow or Black on photo paper—system delivers Kp, C, Mand/or Y & P

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A method of printing an ink jet image comprising separately applyingto an ink jet receiver a colored ink and a substantially colorless ink,wherein the colored ink comprises a cationic coloring agent preparedfrom a colorant dispersed with a cationic oligomer, polymer orsurfactant, and the colorless ink comprises an anionic polymer, andwherein the inks are applied in an overlaying manner.
 2. The method ofclaim 1 wherein the two inks are applied in a simultaneous manner. 3.The method of claim 1 wherein the colored ink is applied andsubsequently the colorless ink is applied in an overlaying manner. 4.The method of claim 1 wherein the ink jet receiver is plain paper. 5.The method of claim 1 wherein the coloring agent of the colored ink is apigment.
 6. The method of claim 1 wherein the coloring agent is black.7. The method of claim 1 wherein coloring agent is cyan.
 8. The methodof claim 1 wherein the coloring agent is magenta.
 9. The method of claim1 wherein the coloring agent is yellow.
 10. The method of claim 1wherein the coloring agent is carbon black.
 11. The method of claim 1wherein the anionic polymer or oligomer in the colorless ink has aweight average molecular weight of 600 to 30,000.
 12. The method ofclaim 1 wherein the e anionic polymer or oligomer in the colorless inkhas an acid number of 50 to
 200. 13. The method of claim 1 wherein theanionic polymer is polyester, polyurethane or polymers derived fromstyrene and/or acrylic acid derivatives.
 14. The method of claim 1wherein the colorless ink comprises at least two anionic polymers. 15.The method of claim 1 wherein the colorless ink comprises at least twodifferent polymers, a first polymer and a second polymer, having aweight average acid number of 70 to
 200. 16. The method of claim 15wherein first polymer has an acid number of 60 to 100 and the secondpolymer has an acid number of 180 to
 240. 17. The method of claim 15wherein the first polymer is a polyurethane polymer that has an acidnumber of 60 to 100 and a molecular weight of greater than 10,000, andthe second polymer is an acrylic polymer that has an acid number greaterthan 180 and a molecular weight of less than 18,000.